In a previous post talking about current temperatures, a point was raised in the comments that both 1998 and 2009 were el Nino years and that this was causing the observed increase in temperatures.
Since I have a desk full of paper work and am looking for ways to avoid it I thought I would play with the data a bit. I used the time period 1900 onwards (since I happen to have an Excel spreadsheet of the GISS data for 1900 onwards) and obtained the el Nino years from this paper.
I had to think about how to remove the el Nino years and still leave a workable dataset, so I decided that I would simply remove the temperature for an el-Nino year and replace it with an average of the year before and after. Not perfect, but a good first approximation.
The following is what I produced.
It is probably hard to see, but the red data set is the years as recorded, the blue data set is the years with the el-Nino averaged out. I have also included statistics for a linear trend through the data. As you can see while several hot years are "cooled", there is very little change in the overall trend. So while el Nino can make years hot, it does not contribute to longterm changes.
I am willing to provide my data to anyone interested. If you want it, e-mail me at john dot croix hat (without the h) hotmail dot com.